1. Field of the Invention
The present invention relates in general to a balloon-type electrode to be inserted into a blood vessel of a heart. More particularly, the present invention relates to a temporary balloon-type electrode adapted for insertion and temporary location in a blood vessel of a heart for determining a suitable place therein for a subsequently inserted and fixated permanent electrode.
2. Description of the Prior Art
When carrying out transvenous heart pacing, in particular transvenous pacing of the left atrium and left ventricle of the heart for achieving a desired coordination of left and right ventricular contraction patterns, a very accurate location of the heart stimulation electrode in coronary sinus or in a peripheral vein is necessary. The stimulation electrode used for this purpose needs to be radially expandable into a fix contact with the interior surface of the blood vessel in question, and it must have a structural configuration which does not obstruct or affect the blood flow through the electrode in any deteriorating manner.
Defibrillation electrodes are known for intravascular implantation in coronary vessels of the heart for delivering defibrillation pulses thereto. For example U.S. Pat. No. 5,170,802 discloses such a radially expandable defibrillation electrode which is initially mounted around an expandable portion of a balloon catheter which is guided by a guide catheter to a desired location for implantation of the electrode. Upon the guide catheter reaching a position adjacent the desired location for implantation, the balloon catheter is advanced out of the distal end of the guide catheter and brought into contact with the inner wall of the blood vessel by inflating the balloon portion, thereby causing the electrode to be permanently deformed by straightening of the zigzag bands thereof so as to remain in contact with the interior of the blood vessel after deflation of the expandable portion of the balloon catheter. The electrode provides an elongated conductive surface in the general form of a hollow cylinder which allows the implantation of a large surface area electrode which may be useful for defibrillation, cardioversion or other stimulation without substantially impeding the flow of blood through the blood vessel. The electrode may also take the form of a so-called resilient stent which by itself may expand radially into contact with the inner wall of the blood vessel when exiting a distal end opening of the guide catheter. Similar prior art solutions are disclosed in e.g. U.S. Pat. Nos. 5,411,546 and 5,431,683.
Once fixed to the interior surface of a blood vessel such prior art electrodes are not easily removable from the implantation site which makes them unsuitable for sensing activities for determining the best pacing/sensing position in the blood vessel for transvenous left-heart pacing/sensing before a stimulation electrode is fixated.
It is an object of the present invention to provide a temporary balloon-type electrode wherein the aforementioned drawbacks of the prior art electrodes are avoided and which is suitable for insertion and temporary location in a blood vessel of a heart for determining by a sensing or mapping procedure an appropriate place therein for a subsequently inserted and fixated, secondary stimulation electrode.
This object is achieved by a balloon-type electrode of the type initially described which has a catheter having a distal end portion and a proximal end portion, an inflatable and deflatable balloon member located at the distal end portion of the catheter and having at least one radially expandable hollow body; at least one electrode surface contact member disposed at a peripheral portion of the hollow body, and flow passages allowing a blood flow to pass the balloon member when inflated.
The inventive electrode has thus a structure which allows a temporary insertion thereof into blood vessels of the heart, such as coronary sinus or peripheral coronary veins, by means of a suitable guide wire or stylet and a subsequent inflation of the or each radially expandable hollow balloon body so as to bring each electrode surface contact member into contact with the interior surface of the blood vessel. In this state, when determining the best position for subsequent transvenous pacing, various criteria need to be fulfilled.
1) The hemodynamic criteria:
a) The position must be determined to optimize the hemodynamical performance of the heart which can be achieved through ECG-analyses to determine that the intended left/right ventricle activation is obtained.
b) Alternatively, this can be determined through ultrasound measurement, which provides a more precise information of the hemodynamnic situation.
c) Left/right blood-pressure curves may also provide valuable information on the hemodynamic situation.
2) Sensing criteria:
The sensing signal must be of acceptable amplitude, typically  greater than 2 mV.
3) Threshold criteria:
The pacing threshold must allow continuous pacing with acceptable energy consumption. The required threshold is in the order of 2 V.
4) Other criteria:
Respiratory stability
QRS-activation pattern
QRS-duration
In the process of finding the most appropriate location for transvenous left-heart stimulation the position of the temporary balloon electrode may be varied by deflating the balloon body, displacing the balloon electrode on the guide wire, and reinflating it at another position where the above-mentioned criteria are again determined and compared. During this temporary fixation and temporary stimulation by means of the balloon-type electrode, the flow passages formed therein ensure sufficient blood flow to pass the balloon member. When good values of these criteria have been obtained for the intended heart stimulation activities, the temporary balloon electrode is removed by sliding it off the guide wire which remains in situ. The exact position for the best heart stimulation may be observed by X-ray fluoroscopy with the help of markers on the remaining guide wire and/or on the balloon electrode. Then the balloon electrode may be replaced by a secondary, permanent stent-type electrode which is guided by the guide wire to the preselected stimulation position and affixed to the interior surface of the blood vessel at that position by a radial expansion of the stent electrode. Finally, the guide wire is removed.
Further features and advantages of the balloon-type electrode of the present invention will be apparent from the following detailed description of the invention in conjunction with the accompanying drawings.